A multiple-input multiple-output (MIMO) wireless communication system may utilize multiple antennas at both a transmitter and a receiver to transmit and receive data and to improve the range and performance of the system. Data packets can be independently and simultaneously transmitted using separate data signals in parallel using separate MIMO channel subcarriers on different transmission antennas. At each receiver antenna, the independent data packets may be combined and the receiver may recover the separate data signals with a decoder. Data transmitted and received using a MIMO system may be modulated using orthogonal frequency division multiplexing (OFDM) or other modulation schemes. Examples of MIMO-OFDM systems include wireless local area networking using the IEEE 802.11n standard, wireless metropolitan area networking using the IEEE 802.16e/j/m standards, mobile phone communications using the 3GPP LTE standard, and other systems.
In a MIMO system, the transmitter may utilize channel state information of a channel subcarrier to perform beamforming. Beamforming is a technique that can increase the directivity of transmitted data packets and the signal-to-noise ratio gain at a receiver. Traditionally, channel state information is maintained by the transmitter using explicit beamforming, where the transmitter sends a sounding packet to the receiver, and in response the receiver feeds back information to the transmitter regarding characteristics of a channel that was used to send the sounding packet. However, this traditional technique may incur system overhead and sacrifice throughput.